The invention relates to tire retreading processes. More specifically, the invention relates to a method and apparatus for balancing a tire during the retread operation.
Producing a uniformly round and balanced tire from a buffed tire casing during the retreading or recapping process is difficult. The worn tire casing may have non-uniformities generated by the stresses during its previous use. The buffing process to remove the worn tread may create out-of-round or radial runout non-uniformities. Further, the original manufacturing process may have built some non-uniformities into the tire casing.
The invention proposes a method and apparatus to apply a new gum layer and tread to a buffed tire casing in a way that compensates for certain non-uniformities present in the tire casing to improve the uniformity of the assembled tire casing and tread. According to the invention, a buffed casing is measured for radial runout and the various relative high and low portions are indexed. The gum layer and tread are applied to the casing in a way that compensates for the radial runout variations. According to a first, preferred embodiment, the casing is positioned so that the gum layer is applied onto the casing beginning at the relatively lowest portion of the crown periphery, and an overlap is formed at this lowest portion. In this way, at least the lowest portion can be partially filled to compensate for the difference in round.
According to another aspect of the invention, the tread strip is applied to the casing so that the joint is positioned at the lowest portion. This provides a heavier or thicker tread layer at the lowest portion of the casing crown, which further compensates for the difference in roundness.
According to yet another aspect of the invention, application of the gum layer may be controlled so that a thicker or thinner layer is applied to the crown proportional to the radial runout variation measurement to compensate for differences in round. The casing with gum applied will have an improved radial runout profile.
Another aspect of the invention involves adjusting the tread strip during application to compensate for radial runout variation. According to this aspect of the invention, the tread strip is stretched as it is applied to the casing so that the thickness of the tread strip is used to compensate for the radial runout variation, the tread being made thinner where the casing radial runout is relatively high and thicker where the casing radial runout is relatively low.
According to another embodiment of the invention, the radial runout measurements of the casing are analyzed as vector quantities and a compensating vector is determined to locate starting points for application of the gum layer and the tread strip. In this embodiment, one or more resultant low portion vectors are determined and indexed for the gum applicator and tread strip applicator. More than one vector may result in cases in which multiple low portions of the same size exist on the tire casing.